This invention relates to leak detection methods and systems, and more particularly, to automotive fuel leak detection using pressure, temperature, and time differentials.
In a vapor handling system for a vehicle, fuel vapor that escapes from a fuel tank is stored in a canister. If there is a leak in the fuel tank, the canister, or any other component of the vapor handling system, fuel vapor could exit through the leak to escape into the atmosphere.
Vapor leakage may be detected through evaporative monitoring. This evaporative monitoring may be performed while an engine is running, where pressure decrease may be analyzed. This type of evaporative monitoring may detect 1 mm and larger leaks, however, it is believed that many parameters influence the accuracy of the diagnosis. Therefore, it is believed that evaporative monitoring when the engine is off is more reliable.
The present invention provides a method of leak detection in a closed vapor handling system of an automotive vehicle, wherein an engine is shut off. The method includes obtaining a start temperature and start pressure, providing an evaluation temperature, calculating a temperature differential between the start temperature and the evaluation temperature, incrementing a time counter if the temperature differential is greater than a temperature control value, computing a pressure differential between the start pressure and an evaluation pressure, and comparing the time counter to a time control value if the pressure differential is not greater than a pressure control value.
The present invention also provides another method of leak detection in a closed vapor handling system of an automotive vehicle, wherein an engine is shut off. This method includes determining whether the engine is off, closing a shut off valve, providing a pressure sensing element, a temperature sensing element, and an engine management system to receive pressure and temperature signals from the pressure sensing element and temperature sensing element, obtaining a start temperature and start pressure, providing an evaluation temperature, calculating a temperature differential between the start temperature and the evaluation temperature, comparing the temperature differential to a temperature control value, incrementing a time counter if the temperature differential is greater than a temperature control value, setting the time counter to zero if the temperature differential is less than or equal to the temperature control value, computing a pressure differential between the start pressure and an evaluation pressure, comparing the pressure differential to the pressure control value, and comparing the time counter to a time control value if the pressure differential is not greater than the pressure control value.
The present invention also provides an automotive evaporative leak detection system. The system includes a pressure sensing element, a temperature sensing element, and a processor operatively coupled to the pressure sensing element and the temperature sensing element and receiving, respectively, pressure and temperature signals therefrom. The processor calculates a temperature differential between a start temperature and an evaluation temperature, increments a time counter, computes a pressure differential between a start pressure and an evaluation pressure, and compares the time counter to a time control value.
The present invention further provides another automotive evaporative leak detection system. This system includes a differential tank pressure sensor located on a conduit between a fuel tank and a canister, a temperature sensor mounted on the fuel tank, a shut off valve located between the canister and an atmosphere, a control valve located between the canister and an engine, and a processor operatively coupled to the pressure sensor and the temperature sensor and receiving, respectively, pressure and temperature signals therefrom. The canister communicates with the engine and the atmosphere, the fuel tank communicates with the engine and the processor opens and closes the shut off valve and the control valve. The processor also calculates a temperature differential between a start temperature and an evaluation temperature, increments a time counter, computes a pressure differential between a start pressure and an evaluation pressure, and compares the time counter to a time control value.